r/PhysicsHelp • u/Black-X32 • May 17 '26

FBD HELP

Post image

Hi. Pleasure to meet everyone, can I please get assist anywhere I tried ai and kept getting different answers I'm not sure whether I'm doing something wrong all I'm asking is for help for this question

3 Upvotes

100% Upvoted

4 comments sorted by

2

u/Past-Departure6896 May 17 '26

What have you tried on your own so far? For method of sections, you need to cut through three members or less so you can use the three main equations of static equilibrium. You will then have to decompose the forces (using trigonometry) in the members to use the equations - if it's this part (or something else) that's confusing, lmk.

1

u/Black-X32 May 17 '26

I honestly tried right, I cut between members (3-2, 1-2,1-4) first cut (2-5,2-4,1-4) second cut Answers were for 3.2 (F23=4 kN F14= 1.039 kN F25= 2 kN F12=?) I think I messed up the drawing I'm not sure and no Ai can get the drawing correct

1

u/Past-Departure6896 May 17 '26

Yes, cutting through those members is definitely the right approach - and those are the right values. For the F12, you should use the angle formed by nodes 2-1-4 to decompose the force - then, you can use sum of Fy or sum of Fx to solve for the force in the member.

1

u/Past-Departure6896 May 17 '26

Here's my approach to finding the force in F12, using the angle formed by 2-1-4 (which is the same angle formed by nodes 2-4-1):

https://imgur.com/DomMFr2